The stability conjecture for infinite set-homogeneous hypergraphs

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Let k≥3k\geq 3, and let HH be an infinite set-homogeneous kk-hypergraph whose theory is stable, meaning that it does not have the order property: there are no formula ϕ(xˉ,yˉ)\phi(\bar{x},\bar{y}), model MM, and sequences (aˉi)i∈ω(\bar{a}_i)_{i\in\omega} and (bˉj)j∈ω(\bar{b}_j)_{j\in\omega} such that M⊨ϕ(aˉi,bˉj)M\models\phi(\bar{a}_i,\bar{b}_j) if and only if i<ji<j. A kk-hypergraph is complete if every kk-element subset is a hyperedge, and its complete complement is obtained by replacing the hyperedge relation with its complement.

The stability conjecture. Any infinite set-homogeneous kk-hypergraph with stable theory is complete or has complete complement.

This predicts that stability forces an infinite set-homogeneous kk-hypergraph to be trivial up to complementation. The supplied text poses the statement without indicating whether it is known or resolved.

References

Primary source

Amir Assari, Narges Hosseinzadeh and Dugald Macpherson, “Set-homogeneous hypergraphs”, arXiv:2202.09613 (2022).

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